The subject matter disclosed herein relates to a laser scanner and in particular to a laser scanner able to vary the density of the measured surface points based on characteristics of the surface geometry.
Laser scanners are a type of device that utilize a coherent light source to measure and determine the three-dimensional coordinates of points on an object. Laser scanners are typically used for scanning closed or open spaces such as interior areas of buildings, industrial installations and tunnels. Laser scanners are used for many purposes, including industrial applications and accident reconstruction applications. A laser scanner can be used to optically scan and measure objects in a volume around the scanner through the acquisition of surface points representing objects within the volume. Such surface points are obtained by transmitting a beam of light onto the objects and collecting the reflected or scattered light to determine the distance, two-angles (i.e. an azimuth and a zenith angle), and optionally a gray-scale value. This raw scan data is collected, stored and sent to a processor or processors to generate a three-dimensional coordinates and an image representing the scanned area or object. In order to generate the image, at least three values are collected for each surface point. These three values may include the distance and two angles, or may be transformed values, such as the x, y, z coordinates.
Some contemporary laser scanners may also include a camera mounted on or integrated into the laser scanner for gathering camera digital images of the environment and for presenting the camera digital images to an operator. By viewing the camera images, the operator can determine the extent of the measured volume and adjust the settings of the laser scanner to measure over a larger or smaller region of space. In addition, the camera digital images may be transmitted to a processor to add color to the scanner image. In order to generate a color scanner image, at least six values (three-positional values such as x, y, z; and color values, such as red, green and blue values or “RGB”) are collected for each surface point.
It should be appreciated, that the acquisition of three-dimensional coordinates of surface points by laser scanners may result in a large volume of data involving millions of surface points. Many of these surface points may not be needed in order to adequately represent objects or surfaces within the scanned volume. Some extraneous data may be removed during postprocessing. However, a large amount of storage space may be taken up in the scanner's local storage device by extraneous data acquired during operation.
In addition, there is a tradeoff between scanning speed and resolution of collected 3D measurement values. It is possible to measure a given region of space in a shorter time with lower resolution or to measure the same region of space in a longer time with higher resolution. The determination of time versus resolution depends on the detail in the object being measured, the relatively rate of change in the surface profile, the amount of noise in the scanner data and the corresponding desired amount of filtering, and the characteristics and size of the object being measured. Today, laser scanners operate by collecting data at a fixed angular speed of the beam sent from the scanner to the object under test. The data is later collected, and if more resolution is needed an additional scan is taken.
Accordingly, while existing laser scanners are suitable for their intended purposes, what is needed is a laser scanner that may dynamically adapt the scanning speed and the density of surface point acquisition based on considerations such as the characteristics of geometric features measured within the scanned volume.